In crude oil and natural gas production process, wastewater (produced water) is produced in large quantities. Mccormack et al. in Mccormack, P., Jones, P., Hetheridge, M. J. and Rowland, S. J. (2001). Analysis of oilfield wastewaters and Production chemicals by electrospray Ionisation multi-stage mass spectrometry (ESI-MSn), Water Reserch. 35(15), 3567-3578 have reported that Wastewater normally contains high concentrations of total n-alkane (TNA), polycyclic aromatic hydrocarbons (PAHs), minerals, radioactive substances, benzenes and phenols.
Extraction technology and reservoir characteristics affect the amount of wastewater production. Campos, J. C., Borges, R. M. H., Oliveira Filho, A. M., Nobrega, R., Sant'Anna Jr, G. L. (2002). Oilfield wastewater treatment by combined microfiltration and biological processes, Water Research, 36, 95-104 have reported that in some sites the volume of wastewater produced may be tenfold the quantity of oil production. It can be estimated that wastewater production in Malaysia is around 5 million barrels per day.
In recent years researchers have concentrated on biological treatment of salty wastewaters specially oilfield wastewater and various prior art documents are available to demonstrate this.
For an example, in US Patent Application published as US20070275450, a culture capable of reducing perchlorate and nitrate in brine solution containing at least 30 g/L NaCl under anaerobic/anoxic conditions was used to demonstrate biological process. In U.S. Pat. No. 6,971,238 B1, an evaporation method used to create steam from wastewater.
In U.S. Pat. No. 6,117,333 an oxidant, ferric ions, and flocculent were used to remove hydrocarbons, arsenic and mercury for treatment of wastewater. This chemical treatment needs high amounts of chemicals.
In U.S. Pat. No. 6,054,050, a process for removing soluble and insoluble organic and inorganic contaminants from refinery wastewater streams employing ultrafiltration and reverse osmosis was provided. To remove divalent and trivalent metal cations prior to being passed to the reverse osmosis a sequential chemical softening system employed to prevent fouling.
In U.S. Pat. No. 5,250,185 to treat oilfield wastewaters, containing boron and solubilized hydrocarbon compounds to reduce boron concentration, a combined method comprising water softening to remove substantially all divalent cations, raising the pH of the liquid above about 9.5, and driving the liquid through a reverse osmosis membrane was used.
As reported in Freire, D. D. C., Cammarota, M. C. and Sant'Anna Jr, G. L. (2000). Biological treatment of oil field wastewater in a sequencing batch reactor, Environmental Technology, 22, 1125-1135, an effluent containing a mixture of oil field wastewater and sewage in different percentages with acclimatized activated sludge microorganisms was treated. In some tests they used a cotton cloth to retain part of the oil and grease in raw wastewater. With 2000 mg/l average Chemical Oxygen Demand (COD) of raw wastewater, maximum removal efficiency was around 70%.
Teller, G. I., Nirmalakhandan, N. and Gardea-Torresdey, J. (2002); Performance evaluation of an activated sludge system for removing petroleum hydrocarbons from oilfield wastewater. Advances in Environmental Research, 6, 455-470 have reported using an activated sludge unit utilizing indigenous microorganisms in a treatment system consisting a skimming and pre-aeration unit followed by biological treatment system. The COD of wastewater from 431±25 mg/l has reduced to 35±11 mg/l and 14±7 mg/l after biological treatment, and clarifier/filtration respectively.
As reported in Zhao, X., Wang, Y., Ye, Z., Borthwick, A., and Ni, J. (2006). Oil field wastewater treatment in Biological Aerated Filter by immobilized microorganisms, Process Biochemistry. 41, 1475-1483, Zhao et al. have investigated the use of B350M and B350 commercial microorganisms (Bio-systems Co.) immobilized on carriers in a pair of Biological Aerated Filter (BAF) to treat wastewater. The COD and TOC of influent wastewater was 124 mg/l and 38 mg/l. Effluent TOC for 13350M and B350 was 8.1 mg/l and 13.3 mg/l respectively.
As reported in Li, Q., Kang C., Zhang, C. (2005). Waste water produced from an oilfield and continuous treatment with an oil-degrading bacterium, Process Biochemistry. 40, 873-877, Li et al. 2005 used Bacillus sp. (M-12) immobilized on polyvinyl alcohol in a continuous wastewater treatment system and cinder column as a final filtration. The COD of the influent decreased from 2600 mg/l to 240 mg/l. Campos et al. 2002 used combined microfiltration as a pretreatment and air-lift biological reactor. Results of biodegradation tests showed that the COD removal efficiency of raw wastewater was about 60% and after microfiltration was 87%. The COD of raw wastewater, after microfiltration and after biological treatment was 2250 mg/l, 1350 mg/l and 230 mg/l respectively.
Funston et al, 2002 as reported in Funston, R., Ganesh, R., and Leong Lawrence Y. C. (2002) Evaluation of technical and economic feasibility of treating oilfield wastewater to create a “New” water resource. Ground Water Protection Council (GWPC) Meeting used a pilot unit consisting of warm softening, coconut shell filtration, cooling (fin-fan), trickling filter, ion exchange and reverse osmosis for treating low IDS (6000 mg/l) wastewater. TOC of raw wastewater decreased from 120 mg/l to 12-24 mg/l after trickling filter.
In most treatment methods, wastewater was physically and chemically pre-filtered before feeding to a biological unit. Microfiltration, skimming and coconut shell filtration were used as physical treatment and warm softening and coagulant were used as chemical treatment. In most of researches proposed treatment methods can not reduce high COD concentration of wastewater (COD more than 2000 mg/l) to less than 200 mg/l, as a result effluent can not meet DOE limits also fluctuation of COD in effluent is very high.
As illustrated above, discharge of wastewater even after treatment using currently available treatment processes has caused pollution to soil, waterways and underground water.
Therefore, it is an object of the present invention to provide a process without any chemical and physical pretreatment, and flexible enough to handle different feed characteristics and easier operation than other biological processes. It is another object of the present invention to provide a process to treat wastewater without large fluctuations in effluent and therefore meet discharge limit standards.